The overall objective is to define the chemical and physical parameters which regulate immune cellular recognition. Plasma membrane vesicles obtained from tumor target cells are being characterized for enzyme activities, extent of glycosylation of H-2 proteins, asymmetric orientation, and interaction with specific antibodies. We will reconstitute purified histocompatibility antigens into defined lipid systems which mimic the environment of the naturally occurring lipids in the plasma membrane. We will test these reconstituted antigens for their ability to inhibit recognition between a specific cytotoxic T cell and its target cell or to act as targets and be lysed directly by cytotoxic T cells.